How is geothermal energy captured? Magma rising from the mantle heats the ground to over 200o
C just 1 km below the surface.
Precipitation falling in the highlands seeps (percolates) down one to three km into the bedrock where it is heated by the hot rocks beneath the surface. In some areas the water is heated to more than 380o
C. The hot
water then rises towards the surface often forming hot springs and steam vents.
In order to use the geothermal energy the rocks have to be drilled to capture the hot water. Cold water is passed through the boreholes where it is heated and returned to the surface. In some areas hot water rises naturally to the surface.
Uses of geothermal energy
Iceland has used geothermal energy since the 1930s. Today five major and many other smaller geothermal power plants exist in Iceland. These produce approximately 29% of the nation's energy (2009).
The geothermal plants produce electricity and hot water which is piped directly to homes and industries.
Geothermal heating also provides heating and hot water for approximately 87% of all buildings in Iceland.
In Iceland’s two largest cities, Reykjavík and Akureyri, pavements and car parks are kept ice-free during winter by underground heating systems.
One of Iceland’s most important usages of geothermal energy is for heating greenhouses. For years, the naturally warm soil has been used for growing potatoes and other vegetables. Horticulture has benefited considerably from geothermal resources, as the heating of greenhouses has increased production and lengthened the growing season.
Geothermal energy has been used in Iceland for drying fish and seaweed for about 25 years. Hot air is blown on the fish and seaweed to dry them out.
Cold water pumped down
Steam and hot water
Hot rock
Hot rock Fig. 24 Capturing geothermal energy in Iceland